A Schottky GaN transistor, which is a type of a HEMT (high electron mobility transistor), may achieve high output and high-speed operations, and therefore is used in a switching circuit configured to perform switching at a high speed, a power circuit, and the like.    [Patent Document 1] Japanese Laid-open Patent Publication No. 2011-101217    [Patent Document 2] Japanese Laid-open Patent Publication No. 2010-109322